Gear lubricant improving agents



3,013,971 GEAR LUBRICANT IMPROVING AGENTS Thomas W. Mastin, Willoughby, Ohio, assignor to The Lubrizol Corporation, Wickliife, Ohio, a corporation of Ohio No Drawing. Filed Feb. 5, 1959, Ser. No. 791,286 4 Claims. (Cl. 252-321) The present invention relates, as indicated, to compositions intended for use in preparing lubricants for relatively moving metal surfaces. More particularly, it re- A lates to compositions intended for the compounding of lubricants for the gears of automotive vehicles.

This application is a continuation-in-part of applicants co-pending application Ser. No. 484,555, filed January 27, 1955 and now abandoned.

The problems of lubricating automotive gears became increasingly acute during the latter part of the decade 1920-1930, when manufacturers began to replace spiral bevel gears with hypoid gears in the rear axles of automotive equipment.

For reasons inherent in their design, hypoid gears permi-t the lowering of the center of gravity and the overall height of vehicles. Coupled with these desirable features, however, were many new lubrication problems. It was found that hypoid gears, unlike spiral bevel gears, could not be lubricated satisfactorily with ordinary mineral oils.

The great pressures existing between the contacting metal surfaces in hypoid gear systems literally squeezed out the mineral oil lubricant, resulting in metal-to-metal contact under extremely high pressures and subsequent deformation and destruction of the gear surfaces.

Early workers in the lubricant art discovered that destructive metal-to-metal contact in hypoid gear systems could be avoided by the addition of certain oil-solublewere promulgated by the Ordnance Department of the US. Army; viz, specification AXS1569, Test Procedure for Determining the Load-Carrying Characteristics of Universal Gear Lubricants Under Conditions of High Speed, and specification AXS-l570, Procedure for Determining the Load-Carrying, Wear, Stability, and Corrosion Characteristics of Universal Gear Lubricants Under;

Conditions of High Torque and Low Speed. Although.

these two tests were originally intended to aid the government and, more particularly, the armed service, branches, in purchasing gear lubricants, they were eventually adopted by the petroleum industry at large as criteria for the selection and purchase o-fgear lubricants destined for the civilian market. For a number of years nited States Patent 0 From an engineering standpoint, the new service requirement encountered is principally one of greatly in-;

the lubricant alone must bear the heightened severity of these tests satisfied the need for tests of good reproduci bility which would simulate in the laboratory, insofar as possible, service conditions encountered in actual use of j However, within recent years, the sharp upward trend.

all types of automotive equipment.

of engine horsepower has placed increasingly severe demands upon the hypoid gears which ultimately transmit the engine power to the drive wheels. These demands are not met with a satisfactory margin of safety by currently available gear lubricants which will pass one or both of the Ordnance Department tests referred to above.

operating conditions if it is to prevent gear failures. This need for a more satisfactory lubricant is particularly critical during the initial break-in period of a vehicle, for it v is then that the gears are most susceptible to deformation.

As more or less a stop-gap measure, manufacturers of automotive equipment have factory-installed lubricants which will protect the gears against severe shock loading, even though such lubricants have been shown to be of little or no value in protecting the gears under high torquelow speed service conditions.

The problem of providing a gear lubricant which will lubricate hypoid gears in a changing operating environment wherein shock load, high speed, and high torque demands are made both cyclically and in sequence on the lubricant is a very difiicult one. The difliculty stems principally from the fact, well known to workers in the lubricant art, that materials which help the lubricant perform its task under one set of operating conditions, say shock loading at high speeds, generally reduce or, in some instances, even nullify the effect of materials added to improve the performance of the lubricant under a different set of operating conditions; e.g., high torque loading at relatively lower speeds.

By effecting a critical balance between the proportions of materials known to be effective under (a) high speed operating conditions, and (b) high torque relatively lower speed operating conditions, prior workers in the lubricant art have been able to produce lubricants which meet the requirements of the aforesaid Army Ordnance high speed and high torque performance tests.

. All of such carefully balanced or compromise lubri cants have not proved amenable to modification, however, so as to enable them to withstand both severe shock loads at high speeds and high torque loads at relatively lower speeds. The addition thereto of materials known to be effective under shock load conditions upsets the carefully balanced lubricant and renders it substantially less effective in a high torque-low speed operating environment.

It is the principal object of the present invention therefore to provide novel improving agents for the production of lubricants which will render satisfactory performance in the hypoid gear systems of modern, highpowered, automotive equipment under severe operating conditions characterized by shock load, high speed, and

high torque demands.

This and related objects of the invention will become apparent as the description of the invention proceeds.

In accordance with the present invention, it has been discovered that this and other objects may be achieved by the use of lubricant improving agents which contain certain critical proportions of both (a) an oil-soluble substituted phosphorodithioic acid containing an organic substituent, and (b) an oil-soluble organic polysulfide.

In a more particular sense, the invention relates to the provision of a liquid, homogeneous improving agent which, when present in gear lubricant compositions, increases the ability thereof to function under high speedshock load as well as high torque conditions of operation,

' consisting of the combination of:

B. an oil-soluble organic polysulfide having at least one sulfur atom bonded only by secondary valence bonds;

said components A and B being present in relative proportions such that when an admixture thereof is dissolved in a solvent therefor in an amount equal to from about 3.5% to about 15% based on the weight of the total solution, said solution will have contributed thereto by said components:

(i) from about 0.20% to about 0.75% phosphorus; and

(ii) from about 0.25% to about 1.0% of chemically combined sulfur which is bonded only by secondary valence bonds.

In a yet more particular sense, the invention relates to the provision of a liquid, homogeneous improving agent which, when present in gear lubricating compositions, increases the ability thereof to function under high speed-shock load as well as high torque conditions of operation, consisting of the combination of:

A. an oil-soluble derivative of a phosphorodithioic acid di-ester selected from the class consisting of the triesters, metal salts, and bis-phosphorodithioates thereof; and

B. an oil-soluble organic polysulfide having at least one sulfur atom bonded only by secondary valence bonds;

said components A and B being present in relative proportions such that when an admixture thereof is dissolved in a solvent therefor in an amount equal to from about 3.5% to about 15% based on the weight of the total solution, said solution will have contributed thereto by said components:

(i) from about 0.3% to about 0.5% phosphorus; and

(ii) from about 0.5% to about 0.9% of chemically combined sulfur which is bonded only by secondary valence bonds.

The relative proportion of phosphorus to sulfur which is bonded only by secondary valence bonds Will preferably be within the range or" from about 1:1 to about 1:2.

In addition to the two characterizing components A and B, the lubricant improving agent and lubricants compounded therefrom may also contain, if desired, auxiliary improving agents such as, for example, rust inhibitors, oiliness agents, viscosity index improvers, and the like. The presence of these and other auxiliary agents, however desirable they may be for their contribution to the qualities of the finished lubricant, is not required to prevent gear deformation under severe operating conditions.

COMPONENT A: THE OIL-SOLUBLE SUBSTI- TUTED PHOSPHORODITHIOIC ACID CONTAIN- ING AN ORGANIC SUBSTITUENT Materials useful as this component are derivatives of phosphorodithioic acid di-esters and may be defined by the following formula:

aO \SX where R and R are the same or different ester radicals and X is the hydrogen equivalent of a radical capable of chemically replacing the acidic hydrogen atom of the phosphorodithioic acid di-ester and is selected from the class consisting of organic radicals and metallic radicals.

In the formula given above for component A, R and R are the same or different aromatic, aliphatic, or cyclo aliphatic radicals, which radicals may be hydrocarbon in nature or contain substituents such as; e.g., chloro, bromo, fiuoro, nitro, alkoxy, thioalkoxy, carboalkoxy, etc., R and R are usually hydrocarbon radicals such as; e.g., aryl, alkaryl, aralkyl, cycloalkyl, and straightor branched-chain alkyl radicals. They are preferably alkyl radicals containing from 1 to about 40 carbon atoms 4 such as; e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, n-amyl, isoamyl, n-hexyl, 4-methyl-2-pentyl, n-octyl, capryl, n-nonyl, 3,5,5-trimethyl-hexyl, dodecyl, hexadecyl, eicosyl, tricosyl, and alkyl radicals of from about 20 to 40 carbon atoms derived from petroleum waxes.

As indicated earlier, R and R may be different ester radicals. A particularly valuable class of phosphorodithioic acid di-esters useful as starting materials for the preparation of component A are those in which (1) R and R are different alkyl radicals,-one containing at least 6 carbon atoms and the other containing less than 6 carbon atoms; or (2) at least two different phosphorodithioic acid di-esters are present, R and R of one acid being alkyl radicals of at least 6 carbon atoms each and R and R of a second acid being alkyl radicals of less than 6 carbon atoms each. These useful phosphorodithioic acid di-esters and their metal salts are disclosed in pending application, Serial No. 251,139, filed October 11, 1951, now US. Patent No. 2,838,555 by Fred C. Goldsmith and having an assignee common to the instant application.

X, as indicated above, is a radical capable of chemically replacing the acid hydrogen atom of the phosphorodithioic acid di-ester and selected from the class consisting of organic radicals and metallic radicals. By the latter statement it is not meant to infer that all organic radicals and/or metallic radicals are fully equivalent for the purposes of this invention, since some are preferred over others for certain uses.

Where X is an organic radical, it is preferably an organic radical containing at least one inorganic element or substituent. More particularly, it is an aromatic or aliphatic radical and preferably an aliphatic radical containing at least one inorganic element such as; e.g., oxygen, sulfur, phosphorus, halogen, nitrogen, and metal. Among the inorganic substituted aliphatic radicals most suitable as X are (1) hydroxyl substituted aliphatic radicals, and (2) aliphatic radicals containing at least two different inorganic elements such as; e.g., phosphorusand-sulfur-substituted aliphatic radicals and metal-andoxygen-substituted aliphatic radicals.

In this group of inorganic substituted aliphatic radicals most suitable as X, a preference exists for monohydroxyalkyl radicals and the anionic radicals of phosphorodithioic acid di-esters.

Thus X may be, for example, one of the following radicals: 2-chloroethyl, Z-hydroxyethyl, 2- and 3-hydroxypropyl, Z-mercaptoethyl, 2- and B-mercaptopropyl, 4- nitrobutyl, 3-hydroxybutyl, 2-cyanopropyl, trichloromethyl, 4-chlorobenzyl, trichlorobenzyl, 2-methyl-4-oxo-2- pentyl, heptyl, capryl, 4-oxo-cyclohexyl, 2-thiobutyl, the anionic radical of di-(4-methyl-2-pentyl) phosphorodithioic acid, the anionic radical of di-(methyl-cyclohexyl) phosphorodi-thioic acid, carbomethoxymethyl, carbomethoxyethyl, hydroxyethoxyethyl, epoxypropyl, 2,4-dihydroxybutyl. carboxymethyl, zinc carboxymethyl, leadcarboxyethyl, etc.

When X is a metallic radical it is usually a polyvalent metal and preferably a heavy metal of atomic weight greater than 50 such as; e.g., zinc, cadmium, barium, strontium, lead, tin, etc., with a particular preference for zinc. It is to be understood that in the case of polyvalent metallic radicals, which radicals contain two or more equivalents of metal, the additional valence bonds of the metal will extend similarly to anions of the phosphorodithioic acid di-ester. Thus, for example, a zinc salt of a phosphorodithioic acid di-ester can be represented by either of the structures below:

and Zn represent, respectively, one hydrogen equivalent and two hydrogen equivalents of zinc.

Specific examples of materials useful as component A are as follows, which examples are presented for purposes of illustration only and are not to be construed as limiting the scope of the invention:

Phosphorodithioic acid tri-esters such as, e.g.:

Di-ethyl 2-chloroethyl phosphorodithioate Di-isopropyl 2-hydroxypropyl phosphorodithioate Di-isopropyl 3-hydroxypropyl phosphorodithioate Di-sec-butyl Z-mercaptopropylphosphorodithioatet Di-n-pentyl 4-nitrobutyl phosphorodithioate Di-(4-methyl-2-pentyl) Z-hydroxypropyl phosphorodithioate Di-(4-methyl-2-pentyl) 3-hydroxypropyl phosphorodithioate a V Di-isopropyl heptyl phosphorodithioate Di-n-hexyl capryl phosphorodithioate Di-nonyl hydroxyethoxyethyl phosphorodithioate Di-lauryl 3 -hydroxybutyl phosphorodithioate Di-(2-ethyl-hexyl) 2-hydroxypropyl phosphorodithioate Di-(Z-ethyl-hexyl) carbomethoxymethyl phosphorodithioate Di-(2-ethyl-hexyl) carbomethoxyethyl phosphorodithioate Di-(4-rnethyl-2-pentyl) carbomethoxyethyl phosphorodithioate Di-(4-methyl-2-pentyl) 2-cyanoethyl phosphorodithioate Di-(4-methyl-2-pentyl) 2-methyl-4-oxo 2 pentyl phosphorodithioate 1 v Di-(4-tert-butyl-phenyl) 2 hydroxy-ethyl phosphorodithioate Di-(4-tert-amyl-phenyl) 3 hydroxy-pentyl phosphorodithioate Di-benzyl 2-mercaptoethyl phosphorodithioate Di-(Z-phenethyl) trichloromethyl phosphorodithioate Di-(2-ethyl-hexyl) zinc-carboxymethyl phosphorodithioate Di-(Z-ethyl-hexyl) lead carboxyethyl phosphorodithioate Bis-phosphorodithioates'such as, e.g., bis-(di-alkyl phosj phorodithioates):

Bis-[di-4 methyl-2-pentylj phosphorodithioate] Bis-[di-(methyl-cyclohexyl) phosphorodithioate] Phosphorodithioic acid di-ester thioanhydrides such as,

Thioanhydride of di-n-butyl phosphorodi thioic acid Metal salts of phosphorodithioic acid di-esters such as, e.g.:

, Barium di-lauryl phosphorodithioate From the foregoing it will be noted that materials of particular utility as component A are derivatives of phosphorodithioic acid di-esters selected from the class consisting of the tri-esters, metal salts, and bis-phosphorodithioates thereof. Ofthis group, a preference exists for;

the zinc salts of phosphorodithioic acid di-esters, with a special preference for zinc salts of di-alkyl esters of phosphorodithioic acid. An eminently suitable group of such zinc salts of di-alkyl esters of phosphorodithioic acid are those in the molecular structure of which there is present a substantial proportion of each of (a) alkyl radicals containing at least 6 carbon atoms, and (b) alkyl radicals containing less than 6 carbon atoms, as disclosed in pending application, Serial No. 251,139, referred to supra.

The preparation of compounds useful as component A is well-known in the art. In most instances, the starting material will be a phosphorodithioic acid di-ester produced bythe reaction of an organic hydroxy body with phosphorus pentasulfide according to the equation:

COMPONENT B: THE OIL-SOLUBLE ORGANIC POLY-SULFIDE HAVING AT LEAST ONE SUL- FUR ATOM BONDED ONLY BY SECONDARY 'VALENCE BONDS Materials useful as this component may be defined broadly by the formula:

wherein R and R represent the same or difierent monoor polyvalent organic radicals bonded to S, x and y are small whole numbers, Sis sulfur, and z is at least 2; said polysulfide further characterized in that at least one of the sulfur atoms therein is bonded only by secondary valence bonds. 7

R and R may be aromatic, aliphatic, or cycloaliphatic and may be hydrocarbon in nature or contain substituents such as; e.g., chloro, fiuoro, bromo, alkoxy, carboalkoxy, nitro, nitroso, hydroxyl, etc. In most instances they are hydrocarbon radicals such as; e.g., alkyl, aralkyl, alkaryl, cycloalkyl, cycloalkenyl, alkenyl, or aryl radicals; however for some uses the presence of organic or inorganic substituents is desirable. Typical illustrations of R and R would include; e.g., benzyl, chlorobenzyl, dichlorobenzyl, phenethyl, phenyl-propyl, propyl, butyl, tertoctyl, ethoxy-ethyl, carbolauroxyethyl, ethylene, trimethylene, butyl phenyl, amylphenyl, octyl-phenyl, nitrophenyl, cyclohexyl, methyl-cyclohexyl, isobutenyl, wtertoctenyl, methoxy-phenyl, ethoxy-naphthyl, amyl-hydroxythey may be 2 or more. The subscript z is at least 2 and generally not more than 7. In certain instances, as in the case of mixed organic polysulfides, it may be a non-integral member such as; e.g., 3.3 or 4.6.

By the phrase sulfur atom bonded only by secondary valence bonds" I mean a sulfur atom which is bonded only to one or more sulfur atoms in the polysulfide molecule and is thus devoid of valence bonds extending to the organic radicals in the polysulfide molecule. The exact nature of such secondary valence bonds is not clearly understood, but it is known that they are much weaker than the covalent bond which exists between a sulfur atom and a carbon atom of an organic radical in an organic polysulfide.

Due to the relatively weak attachment of sulfur atoms which are bonded only by secondary valence bonds, such sulfur is more readily given up by the molecule; i.e., is more reactive chemically, than sulfur which is bonded to a carbon atom of an organic radical. The very fact that such sulfur is chemically reactive facilitates its determination. For example, a test sample of the organic polysulfide may be treated with reagents which are known to react with and thus to remove reactive sulfur such as; e.g., warm aqueous caustic solutions, warm aqueous solutions of metallic monosulfides, finely divided metals such as copper, lead, iron, silver, etc. The loss in sulfur content of the test sample of organic polysulfide after such treat ment corresponds to the amount of reactive sulfur originally present; i.e., that sulfur which is bonded only by secondary valence bonds.

Thus it is possible to characterize an organic polysulfide both by its content of (a) total sulfur; i.e., sulfur in all forms, and (b) sulfur bonded only by secondary valence bonds. The discovery that certain critical amounts of the kind of sulfur indicated in (b) must be present in my lubricants constitutes one of the principal features of my invention.

The following partial structures illustrate some of the many arrangements which sulfur atoms can assume in organic polysulfides. In each of these partial structures the presence of an asterisk next to a sulfur atom indicates that such sulfur atom is held in the molecule by secondary valence bonds only:

From a study of the structures given above, it will be apparent that organic polysulfides of like molecular weight and containing the same percentages of chemical elements may possess widely different amounts of reactive sulfur depending on the mode of attachment of the sulfur atoms within the molecule. Those structures which possess the largest number of sulfur atoms bonded only by secondary valence bonds will possess the highest percentage of reactive sulfur.

Specific examples of organic polysulfides which contain at least one sulfur atom bonded only by secondary valence bonds and which are useful as Component B in lubricants of this invention are, for example:

Di-benzyl trisulfide Di-benzyl tetrasulfide Di-benzyl polysulfides containing an average of 4.6 sulfur atoms per molecule Di-benzyl pentasulfide Di-benzyl hexasulfide Monochloro di-benzyl tetrasulfide Di-(4-chlorobenzyl) tetrasulfide Bis-(2,4-dichlorobenzyl) tetrasulfide Di-phenethyl tetrasulfide Diphenyl trisulfide Di-(isopropyl-phenyl) tetrasulfide Di-(tert-octyl-phenyl) tetrasulfide Di-(alpha-naphthyl) trisulfide Di-(amyl-hydroxyphenyl) tetrasulfide Di-(butyl-chlorophenyl) trisulfide Di-tert-butyl tetrasulfide Di-n-hexyl pentasulfide Di-tert-octenyl tetrasulfide Di-tert-octyl trisulfide Di-(methyl-cyclohexyl) pentasulfide Di-(cyclohexyl) tetrasulfide Turpentine'polysulfides containing an average of 2.6

sulfur atoms per molecule Amyl-phenyl cyclohexyl trisulfide Lauryl ethyl tetrasulfide Pine oil polysulfides containing an average of from 2 to 3 sulfur atoms per molecule Di-wax polysulfides containing an average of from 2 t0 4 sulfur atoms per molecule The preparation of materials useful as component B may be accomplished by any of the many different processes which are known and disclosed in the art including, for example, the reaction of halogen-bearing organic compounds with alkali metal polysulfides, the reaction of mercaptans with sulfur and/or sulfur halides, the reaction of .saturated and unsaturated hydrocarbons with sulfur and/or sulfur halides, the reaction of organic monosulfides with sulfur, etc.

Auxiliary improving agents As previously indicated, there may also be present in our lubricants certain auxiliary improving agents such as, for example, detergents, rust-preventatives, film strength agents such as halogenated organic compounds, oiliness 9 agents such as fatty oils and sulfurized fatty oils, pour point depressors, foam inhibitors, viscosity index improvers, oxidation inhibitors, odor irnprovers and the like. Included among the many materials useful for these various purposes are the following:

Detergents such as metal salts of petroleum naphthenic acids, petroleum sulfonic acids, the higher fatty acids, etc.; rust-preventatives such as basic metal petroleum sulfonates, metal phenol-ates, organic amines, benzyl thiocyanate, etc; film strength agents such as chlorinated parafiin waxes containing tom 20 to 70% chlorine, chlorinated eicosane containing from 50 to 60% chlorine, hexac-hloro-diphenyl ether, polychlorobiphenyl, etc.; oiliness agents such as olein, methyl olcate, oleic acid, sulfurized and non-sulfurized sperm oil, corn oil, etc.; pour point depressors such as wax-alkylated naphthalene or phenanthrene, etc.; foam inhibitors such as the polymeric di-alkyl silicones, etc; and viscosity index improvers such as polymerized and co-polymerized alkyl methacrylates, polymerized butylenes, etc.

It is to be understood, however, that the use of any of such auxiliary agents is optional and not required in our lubricants to prevent the deformation of gearsurfaces.

The oil base The lubricating oil base in which the characterizing components A and B of this invention and any desired auxiliary agents are incorporated may be of synthetic, vegetable, animal, or mineral origin. Because of their low cost, availability, and desirability, the mineral oils; i.e., those derived from petroleum, find the widest application in the lubricant art.

There are at the present time sundry mineral oils, each best suited from the standpoint of viscosity and other properties for different climates and operating environments. The oil base of a lubricating composition of the present invention will preferably comprise a mineral lubricating oil having characteristics now well recognized as best suited for such environment and climate.

In Table I following, the characteristics of mineral lubricating oils best suited for a given environment and climate are disclosed. The actual upper limit of preferred viscosity index is infinite for most uses. The values given in the table for viscosity index represent current commercial maximum values.

TABLE I Application in Type of climate Automotive Industrial gears gears Artie: Degrees F. Degrees F.

Preferred viscosity range 1 30-80l210 301,000/2l0 Flash point preferably no lower than 300 300 Pour point preferably no higher than -30 10 Temperate:

Preferred viscosity range 1 50-140/210 502,000/2l0 Flash point preferably no lower than 325 325 Pour point preferably no higher than 20 Tropical:

Preferred viscosity range 1 80-200/210 802,000/21O Flash point preferably no lower than. 350 325 Pour point preferably no higher than. 20 30 Preferred viscosity index for all climates (Dean and Davis scale) 1 Expressed in Saybolt Universal seconds atthe indicated temperature.

Lubricants and lubricant improving agents I As indicated previously, a number of hypoid gear lubricants representative of the several fundamental types which are commercially available were first investigated'to determine their effectiveness in preventing deformation of gear surfaces in an operating environment characterized by severeshoc loads at high'speeds andhigh torque loads at relatively lower speeds.

Full-scale performance tests; i.e., tests using standard automotive equipment, employed in this connection included the Army Ordance AXS-1569 high speed and AXS-l570 high torque tests and, in addition, a new severe shock test using a 1953 model Buick passenger car equipped with a torque converter transmission of the Dynafiow variety.

The latter test, termed for convenience the Buick Shock Test, is one of almost unbelievable severity. It

is carried out in the laboratory by mounting the rear drive wheels of the car on a heavy shaft which is free to revolve and which is designed to simulate the inertia of the car on a level highway. Although the test could conceivably be conducted on the open road, the severe operating conditions specified in its procedure would make such a course extremely hazardous.

In carrying out the test, the rear axle of the car is filled to the specified level with the desired test lubricant and the car is run for the equivalent of 19 miles at 40-50 mph. to break in the new gears. The car is then accelerated from 0 to 70 mph. and decelerated to 0 m.p.h. with the transmission in drive position. If no unusual noise is detected in the rear axle, the car is subjected to a high speed evaluation comprising 10 cycles of acceleration and deceleration, 0 to 70 to 0 m.p.h., with the transis shifted abruptly to the low position. From the preceding description, it is apparent to one familiar with automotive equipment that shock loads of extreme severity are placed upon the coast and drive surfaces of the hypoid gear teeth.

After the shock portion of the test is completed, the high speed evaluation described earlier and comprising 10 cycles of acceleration and deceleration is repeated.

The car is stopped and the pinion and ring gears are removed and inspected for evidence of deformation such as rippling, ridging, spalling, and scoring. These terms define certain specific kinds of deformation which are readily distinguished from each other by trained mechanics. free from deformation, the lubricant is said to have passed the test.

Table II includes the results obtained on commercially available hypoid gear lubricants in the three full-scale tests which have been described. The lubricants are defined by chemical type in terms which are familiar to those in the lubricant art. It will be noted that none of the lubricants gave satisfactory performance in all of the tests, even though several satisfied the less rigorous requirements of the two well-known Army Ordance tests.

If such inspection shows the gear teeth to be These results point up the critical situation which 1 1 preceded the present discovery; viz., that no hypoid gear lubricant was available which would withstand both the rigors of shock loads at high speeds and high torque loads at relatively lower speeds.

12 Additional examples of lubricants of the invention are disclosed in Table IV. These are presented for purposes of illustration only and are not to be construed as limiting the scope of the invention, particularly with re- As stated hereinbefore, lubricants capable of giving 5 spect to the inclusion of optional axuiliary improving satisfactory performance under these extremes of operatagents such; e.g., detergents, oiliness agents, foam ining conditions can be made by incorporating therein hibitors, certain critical proportions of two characterizing come numerlcal al es I p en eses; 6% (0.37% P) ponents; viz, (A) an oil-soluble substituted phosphorodiand S), f0110W111g Q chal'flcterlzmg thioic acid containing an organic substituent, and (B) an 10 POHEHtS A d B m lcate, respectively, the percent phosoil-soluble organic polysulfide having at least one sulfur Phofus 311d p f sulfur bondefl only y Secondary atom bonded only by secondary alen b0 d valence bonds imparted to the finished lubricant by the Table III includes test data on many lubricants con- Particular Componenttaining the characterizing component A and B of the TABLE IV present invention in amounts which either come Within Lubri- Percent or fall outside of the ranges found to be critical for each. cant by Composition The tests employed were the Buick Shock test, the weght Army Ordance AXS-1570 high torque test, and the SAE 6 88 s W 90 1 b t 1 .0 gear u rican. Extreme-Pressure Lubricant test at 1000 r.p.m. Army M Zinc dmaurylphosphowdithmte (037% Ordance test AXS-1J69 was not employed in these studies 17 92A; 1s) i-]t:erg6butyl1trgs11ilfidte (0.91% see. s

r. Q0111 .1 ICafl Smce It had b determined a any iubncant whfch 3.1 Ziiic dHtert-amyl-plicnyl) pliosphorodithioate passed the Buick Shock test, which test includes a high 3 2 (0.21 7% P). 1 H Ind 0 S speed evaluation, would always pass the less severe AXS- 18 1 35 rg ggggfig g gifg e 1569 test. 2.4 1Z)i nc di-airliyl phospllf plrodlthioate (0.25% P).

The SAlE Extreme-Pressure Lubricant test included in 19 $13 5 (14% Table III is a test which is well-known in the lubricant 2-3 g aj g giggi fli lfi. art. It is carried out on the SAE Lubricant machine in jg g i l i i su'llfonam a 0. 005 met 1 s cone p0 ymer.

the manner set forth on page 45 of A.S.T. M. Bulletin 20 89'17 SAE 90 gwmbrmm' No. 181, April 1952. It was found that lubricants which 4.4 ZiEJe ZdWi;(gnethyl-Z-pentyl) phosphorodlthlonte failed this test; i.e., would not sustain the full 590-600 agma 'oi uifiaos containing an average 01 pounds load, also failed the Buick Shock test. Since it o 4 g i per olecule (0.68% sec. 5) was not feasible to conduct Buick Shock tests on all of 2 313 r l i ii r nattd 0505;513 110 containing 50% chlorine.

1 87.57 Ogcar u rican the large number of lubricants investigated, the SA 4'4 Zinc di-(4-m thy1-2-penty1) phosphorodithionte test was employed to screen out lubricants which would 2 73 D (0t.)42% P). ma t m f l- OHZY D0 F511 (.5 0011 all] g 811 average 0 not pass the fO er St- 4.6 sulfur atoms per molecule (0.68% sec. S).

It will be noted that in every instance when one or g g ggg f vgi g g conmmng 507 chlorine both of the two characterizing components A and B 22 851s 11 g l a l dthi t (057 1)) 8.0 in i-oe y piospioro i on e was present in an amount falling outside of the critical Di-(Z-nnphthyl) trisulfide (0.5%sec. s

range disclosed herein, the lubricant failed to give satis- 40 gptfifitcgltzmlllllieflcl lprylgte. t

factory performance. On the other hand, when these 23 5 g h g ggfi mm same components were each present in a lubricant in g ggg gfiggig -gggjg g g g igg y amounts within the range found to be operative, the 0.1 Di-tert-butylhexasulfide(0.3% sec.S).

lubricant was effective in preventing gear deformation 15 gff under both shock loads at high speeds and high torque 24 l 9 r g r t 2b are th 1 h loads at relatively lower speeds. For convenient identi- 3 7 D f lfi w il i r d m 7 7 y b) p 05 i-pienet iy te rasu l c sec.

2 gqgh. E g i g ag aggiisg z f; m Table In have 0.5 Basic calcium petroleum SHHOXSJBKO.

ee 1 ma e TABLE In [All percentages of improving agents are by weight based on the total lubricant] Component A materials employed:

A1=1.inc di-org:inopliospliorodithloate made by neutralizing a mtrture of 40 mole-percent of dl-lsopropyl phosphorodlthlole acid and molepercent of di-(4-metl1yl-2-pcntyl) phosphorodithioic acid with zinc oxide.

A2=zlnc di-(4mcthyl-2-pentyl) phosphoroditliioate.

A3=di-(4-methyl-2-pentyl) hydroxypropyl phosphorodithloate.

A4=BisIdi-(4-methyl-2-pentyl) phosphorodithioate]. Component B materials employed:

B1=monochlor dibeiizyl tetrosulflde.

B- =di-benzyl polysulfides containing an average of 4.6 sulfur atoms per molecule. B3=turpentine polysulfides containing an average of 2.6 sulfur atoms per molecule.

[SAE 90 rode gear lubricant containing the indicated kinds and amounts of improving agents] Component A Component B Test Lubricant No. Percent P Percent SAE test AXS-1570 Kind Percent contributed Kind Percent sec. S c011- at 1,000 Buick high to lube tributed r.p.m. shock torque to lube l 1 Percent sec. S=perceut sulfur bonded only by secondary valence bonds.

It is common practice in the lubricant additive in dustry to provide a liquid, homogeneous improving agent concentrate containing high percentages of one or more separate improving agents and, optionally, a proportion of a mineral oil, preferably one of low viscosity. Such concentrates dissolve readily in lubricating oil bases and minimize the problems associated with handling, storage, and transportation. A further benefit in cases Where two or more separate improving agents are to be incorporated in the oil base is that the relative proportions of the several improving agents can be adjusted within the concentrate by the manufacturer. Then in preparing the finished lubricant, a single addition of only one concentrate need be made to the oil base to impart thereto the desired improving agents in predetermined relative proportions.

Concentrates intended for compounding with an oil base to yield lubricants of the present invention will always contain the two previously identified characterizing components A and B and optionally:

(1) certain desired auxiliary improving agents: and

(2) a proportion, generally from about to about 70% by weight based on the total concentrate, of a lowviscosity mineral oil.

As previously indicated, components A and B will be present in such relative proportions in the concentrate that when the concentrate is incorporated in the lubricant, such lubricant will have contributed thereto by said components:

(1) from about 0.20% to about 0.75% and preferably from about 0.3% to about 0.5% phosphorous; and

(2) from about 0.25% to about 1.0% and preferably from about 0.5% to about 0.9% of chemically combined sulfur which is bonded only by secondary valence bonds.

Depending on the particular components A and B employed, the presence of auxiliary improving agents, and, in some instances, the presence of mineral oil in the concentrate, the amount thereof required to impart to the lubricant the necessary percent phosphorus and percent sulfur bonded only by secondary valence bonds will vary considerably. Generally an amount of the concentrate equal to from about 3.5% to about based on the weight of the total lubricant will be suitable.

Other modes of applying the principle of the invention may be employed, change being made regarding the details described, provided that the features stated in any of the following claims or the equivalent thereof be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A liquid, homogeneous improving agent which, when present in gear iubricant compositions, increases the ability thereof to function under high speed-shock load as well as high torque conditions of operation, consisting of the combination of:

A. an oil-soluble zinc salt of a dialkyl phosphorodithioic acid di-ester having from 1 to about 40 carbon atoms in each alkyl group, and

B. an oil-soluble, substantially hydrocarbon organic polysulfide having from 2 to 7 sulfur atoms and having at least one sulfur atom bonded only by secondary valence bonds said organic polysulfide being selected from the group consisting of turpentine polysulfides and pine oil polysulfides;

said components A and B being present in relative proportions such that when an admixture thereof is dissolved in a solvent therefor in an amount equal to from about 3.5% to about 15% based on the Weight of the total solution, said solution will have contributed thereto by said components:

(i) from about 0.20% to about 0.75% phosphorus;

and

(ii) from about 0.25% to about 1.0% of chemically combined sulfur which is bonded only by secondary valence bonds.

2. The improving agents of claim 1 further characterized in that the relative proportion of phosphorus to sulfur which is bonded only by secondary valence bonds is Within the range of from about 1:1 to about 1:2.

3. The improving agent of claim 1 further characterized in that component B is a turpentine polysulfide.

4. The improving agent of claim 1 further characterized in that component A is a zinc salt of a di-alkyl ester of phosphorodithioic acid in the molecular structure of which there is present a substantial proportion of each of (a) alkyl radicals containing at least 6 carbon atoms, and (12) alkyl radicals containing less than 6 carbon atoms.

References (Iited in the file of this patent UNITED STATES PATENTS 2,157,452 Humphreys May 9, 1939 2,186,271 Pevere Jan. 9, 1940 2,192,874 Smith et al. Mar. 5, 1940 2,205,858 Mikeska et al. June 25, 1940 2,343,831 Osborne Mar. 7, 1944 2,364,284 Freuler Dec. 5, 1944 2,382,115 Stucker Aug. 14, 1945 2,514,625 Clausen et al. July 11, 1950 2,689,220 Mulvany Sept. 14, 1954 2,723,236 Assefi et al. Nov. 8, 1955 2,838,555 Goldsmith June 10, 1958 FOREIGN PATENTS 679,465 Great Britain Sept. 17, 1952 679,466 Great Britain Sept. 17, 1952 689,759 Great Britain Apr. 1, 1953 

1. A LIQUID, HOMOGENEOUS IMPROVING AGENT WHICH, WHEN PRESENT IN GEAR LUBRICANT COMPOSITIONS, INCREASES THE ABILITY THEREOF TO FUNCTION UNDER HIGH SPEED-SHOCK LOAD AS WELL AS HIGH TORQUE CONDITIONS OF OPERATION, CONSISTING OF THE COMBINATION OF: A. AN OIL-SOLUBLE ZINC SALT OF A DIALKYL PHOSPHORODITHIOIC ACID DI-ESTER HAVING FROM 1 TO ABOUT 40 CARBON ATOMS IN EACH ALKYL GROUP, AND B. AN OIL-SOLUBLE, SUBSTANTIALLY HYDROCARBON ORGANIC POLYSULFIDE HAVING FROM 2 TO 7 SULFUR ATOMS AND HAVING AT LEAST ONE SULFUR ATOM BONDED ONLY BY SECONDARY VALENCE BONDS SAID ORGANIC POLYSULFIDE BEING SELECTED FROM THE GROUP CONSISTING OF TURPENTINE POLYSULFIDES AND PINE OIL POLYSULFIDES, SAID COMPONENTS A AND B BEING PRESENT IN RELATIVE PROPORTIONS SUCH THAT WHEN AN ADMIXTURE THEREOF IS DISSOLVED IN A SOLVENT THEREFOR IN AN AMOUNT EQUAL TO FROM ABOUT 3.5% TO ABOUT 15% BASED ON THE WEIGHT OF THE TOTAL SOLUTION, SAID SOLUTION WILL HAVE CONTRIBUTED THERETO BY SAID COMPONENTS: (I) FROM ABOUT 0.20% TO ABOUT 0.75% PHOSPHORUS, AND (II) FROM ABOUT 0.25% TO ABOUT 1.0% OF CHEMICALLY COMBINED SULFUR WHICH IS BONDED ONLY BY SECONDARY VALENCE BONDS. 